Life and health sciences are key application areas for immersive analytics. This spans a broad range including medicine (e.g., investigations in tumour boards), pharmacology (e.g., research of adverse drug reactions), biology (e.g., immersive virtual cells) and ecology (e.g., analytics of animal behaviour). We present a brief overview of general applications of immersive analytics in the life and health sciences, and present a number of applications in detail, such as immersive analytics in structural biology, in medical image analytics, in neurosciences, in epidemiology, in biological network analysis and for virtual cells.

Tracking the temporal evolution of features in time-varying data is a key method in visualization. For typical feature definitions, such as vortices, objects are sparsely distributed over the data domain. In this paper, we present a novel approach for tracking both sparse and space-filling features. While the former comprise only a small fraction of the domain, the latter form a set of objects whose union covers the domain entirely while the individual objects are mutually disjunct. Our approach determines the assignment of features between two successive time-steps by solving two graph optimization problems. It first resolves one-to-one assignments of features by computing a maximum-weight, maximum-cardinality matching on a weighted bi-partite graph. Second, our algorithm detects events by creating a graph of potentially conflicting event explanations and finding a weighted, independent set in it. We demonstrate our method's effectiveness on synthetic and simulation data sets, the former of which enables quantitative evaluation because of the availability of ground-truth information. Here, our method performs on par or better than a well-established reference algorithm. In addition, manual visual inspection by our collaborators confirm the results' plausibility for simulation data.

This chapter overviews the application of immersive analytics to simulations of built environments through three distinct case studies. The first case study examines an immersive analytics approach based upon the concept of “Virtual Production Intelligence” for virtual prototyping tools throughout the planning phase of complete production sites. The second study addresses the 3D simulation of an extensive urban area and the attendant immersive analytic considerations in an interactive model of a sustainable city. The third study reviews how immersive analytic overlays have been applied for virtual heritage in the reconstruction and crowd simulation of the medieval Cambodian temple complex of Angkor Wat.

@Inbook{Chandler2018,author="Chandler, Tomand Morgan, Thomasand Kuhlen, Torsten Wolfgang",editor="Marriott, Kimand Schreiber, Falkand Dwyer, Timand Klein, Karstenand Riche, Nathalie Henryand Itoh, Takayukiand Stuerzlinger, Wolfgangand Thomas, Bruce H.",title="Exploring Immersive Analytics for Built Environments",bookTitle="Immersive Analytics",year="2018",publisher="Springer International Publishing",address="Cham",pages="331--357",abstract="This chapter overviews the application of immersive analytics to simulations of built environments through three distinct case studies. The first case study examines an immersive analytics approach based upon the concept of ``Virtual Production Intelligence'' for virtual prototyping tools throughout the planning phase of complete production sites. The second study addresses the 3D simulation of an extensive urban area (191 km{\$}{\$}^2{\$}{\$}) and the attendant immersive analytic considerations in an interactive model of a sustainable city. The third study reviews how immersive analytic overlays have been applied for virtual heritage in the reconstruction and crowd simulation of the medieval Cambodian temple complex of Angkor Wat.",isbn="978-3-030-01388-2",doi="10.1007/978-3-030-01388-2_11",url="https://doi.org/10.1007/978-3-030-01388-2_11"}

Personal space (PS), the flexible protective zone maintained around oneself, is a key element of everyday social interactions. It, e.g., affects people's interpersonal distance and is thus largely involved when navigating through social environments. However, the PS is regulated dynamically, its size depends on numerous social and personal characteristics and its violation evokes different levels of discomfort and physiological arousal. Thus, gaining more insight into this phenomenon is important.

We contribute to the PS investigations by presenting the results of a controlled experiment in a CAVE, focusing on German males in the age of 18 to 30 years. The PS preferences of 27 participants have been sampled while they were approached by either a single embodied, computer-controlled virtual agent (VA) or by a group of three VAs. In order to investigate the influence of a VA's emotions, we altered their facial expression between angry and happy. Our results indicate that the emotion as well as the number of VAs approaching influence the PS: larger distances are chosen to angry VAs compared to happy ones; single VAs are allowed closer compared to the group. Thus, our study is a foundation for social and behavioral studies investigating PS preferences.

During free exploration of an unknown virtual scene, users often miss important parts, leading to incorrect or incomplete environment knowledge and a potential negative impact on performance in later tasks.
This is addressed by wayfinding aids such as compasses, maps, or trails, and automated exploration schemes such as guided tours.
However, these approaches either do not actually ensure exploration success or take away control from the user.

Therefore, we present an interactive assistance interface to support exploration that guides users to interesting and unvisited parts of the scene upon request, supplementing their own, free exploration.
It is based on an automated analysis of object visibility and viewpoint quality and is therefore applicable to a wide range of scenes without human supervision or manual input.
In a user study, we found that the approach improves users' knowledge of the environment, leads to a more complete exploration of the scene, and is also subjectively helpful and easy to use.

When interacting and communicating with virtual agents in immersive environments, the agents’ behavior should be believable and authentic. Thereby, one important aspect is a convincing auralizations of their speech. In this work-in progress paper a study design to evaluate the effect of adding directivity to speech sound source on the perceived social presence of a virtual agent is presented. Therefore, we describe the study design and discuss first results of a prestudy as well as consequential improvements of the design.

Various factors influence the degree of cybersickness a user can
suffer in an immersive virtual environment, some of which can be
controlled without adapting the virtual environment itself. When
using HMDs, one example is the size of the field of view. However,
the degree to which factors like this can be manipulated without
affecting the user negatively in other ways is limited. Another prominent
characteristic of cybersickness is that it affects individuals very
differently. Therefore, to account for both the possible disruptive
nature of alleviating factors and the high interpersonal variance, a
promising approach may be to intervene only in cases where users
experience discomfort symptoms, and only as much as necessary.
Thus, we conducted a first experiment, where the field of view was
decreased when people feel uncomfortable, to evaluate the possible
positive impact on sickness and negative influence on presence.
While we found no significant evidence for any of these possible
effects, interesting further results and observations were made.

The concept of personal space is a key element of social interactions. As such, it is a recurring subject of investigations in the context of research on proxemics. Using virtual-reality-based experiments, we contribute to this area by evaluating the direct effects of emotional expressions of an approaching virtual agent on an individual’s behavioral and physiological responses. As a pilot study focusing on the emotion expressed solely by facial expressions gave promising results, we now present a study design to gain more insight.

Fluid artwork refers to works of art based on the aesthetics of fluid motion, such as smoke photography, ink injection into water, and paper marbling. Inspired by such types of art, we created Fluid Sketching as a novel medium for creating 3D fluid artwork in immersive virtual environments. It allows artists to draw 3D fluid-like sketches and manipulate them via six degrees of freedom input devices. Different sets of brush strokes are available, varying different characteristics of the fluid. Because of fluid's nature, the diffusion of the drawn fluid sketch is animated, and artists have control over altering the fluid properties and stopping the diffusion process whenever they are satisfied with the current result. Furthermore, they can shape the drawn sketch by directly interacting with it, either with their hand or by blowing into the fluid. We rely on particle advection via curl-noise as a fast procedural method for animating the fluid flow.

In this work, we describe a hybrid, hand-based interaction metaphor that makes remote and close objects
in an HMD-based immersive virtual environment (IVE) seamlessly accessible. To accomplish this, different
existing techniques, such as go-go and HOMER, were combined in a way that aims for generality,
intuitiveness, uniformity, and speed. A technique like this is one prerequisite for a successful integration
of IVEs to professional everyday applications, such as data analysis workflows.

In this interactive demo, we present our Fluid Sketching application as an innovative virtual reality-based interpretation of traditional marbling art. By using a particle-based simulation combined with natural, spatial, and multi-modal interaction techniques, we create and extend the original artistic work to build a comprehensive interactive experience. With the interactive demo of Fluid Sketching during Mensch und Computer 2018, we aim at increasing the awareness of paper marbling as traditional type of art and demonstrating the potential of virtual reality as new and innovative digital and artistic medium.

Virtual Environments: Current Topics in Psychological Research (VECTOR) workshop, 2018

Personal Space (PS) is regulated dynamically by choosing an appropriate interpersonal distance when navigating through social environments. This key element in social interactions is influenced by numerous social and personal characteristics, e.g., the nature of the relationship between the interaction partners and the other’s sex and age. Moreover, affective contexts and expressions of interaction partners influence PS preferences, evident, e.g., in larger distances to others in threatening situations or when confronted with angry-looking individuals. Given the prominent role of emotional expressions in our everyday social interactions, we investigate how emotions affect PS adaptions.

Dissipation elements (DE) define a geometrical structure for the analysis of small-scale turbulence. Existing analyses based on DEs focus on a statistical treatment of large populations of DEs. In this paper, we propose a method for the interactive visualization of the geometrical shape of DE populations. We follow a two-step approach: in a pre-processing step, we approximate individual DEs by tube-like, implicit shapes with elliptical cross sections of varying radii; we then render these approximations by direct ray-casting thereby avoiding the need for costly generation of detailed, explicit geometry for rasterization. Our results demonstrate that the approximation gives a reasonable representation of DE geometries and the rendering performance is suitable for interactive use.

International Conference on Digital Human Modeling and Applications in Health, Safety, Ergonomics and Risk Management 2017

Understanding multi-dimensional data and in particular multi-dimensional dependencies is hard. Information visualization can help to understand this type of data. Still, the problem of how users gain insights from such visualizations is not well understood. Both the visualizations and the users play a role in understanding the data. In a case study, using both, a scatterplot matrix and a HyperSlice with six-dimensional data, we asked 16 participants to think aloud and measured insights during the process of analyzing the data. The amount of insights was strongly correlated with spatial abilities. Interestingly, all users were able to complete an optimization task independently of self-reported understanding of the data.

3D-Polarized Light Imaging (3D-PLI) provides data that enables an exploration of brain fibers at very high resolution. However, the visualization poses several challenges. Beside the huge data set sizes, users have to visually perceive the pure amount of information which might be, among other aspects, inhibited for inner structures because of occlusion by outer layers of the brain. We propose a clustering of fiber directions by means of spherical harmonics using a level-of-detail structure by which the user can interactively choose a clustering degree according to the zoom level or details required. Furthermore, the clustering method can be used for the automatic grouping of similar spherical harmonics automatically into one representative. An optional overlay with a direct vector visualization of the 3D-PLI data provides a better anatomical context.

Immersive data analytics as an emerging research topic in scientific and information visualization has recently been brought back into the focus due to the emergence of low-cost consumer virtual reality hardware. Previous research has shown the positive impact of immersive visualization on data analytics workflows, but in most cases, insights were based on large-screen setups. In contrast, less research focuses on a close integration of immersive technology into existing, i.e., desktop-based data analytics workflows. This implies specific requirements regarding the usability of such systems, which include, i.e., the prevention of cybersickness. In this work, we present a prototypical application, which offers a first set of tools and addresses major challenges for a fully immersive data analytics setting in which the user is sitting at a desktop. In particular, we address the problem of cybersickness by integrating prevention strategies combined with individualized user profiles to maximize time of use.

Applications of Virtual Reality (VR) have been repeatedly explored with the goal to improve the data analysis process of users from different application domains, such as architecture and simulation sciences. Unfortunately, making VR available in professional application scenarios or even using it on a regular basis has proven to be challenging. We argue that everyday usage environments, such as office spaces, have introduced constraints that critically affect the design of interaction concepts since well-established techniques might be difficult to use.
In our opinion, it is crucial to understand the impact of usage scenarios on interaction design, to successfully develop VR applications for everyday use. To substantiate our claim, we define three distinct usage scenarios in this work that primarily differ in the amount of mobility they allow for. We outline each scenario's inherent constraints but also point out opportunities that may be used to design novel, well-suited interaction techniques for different everyday usage environments. In addition, we link each scenario to a concrete application example to clarify its relevance and show how it affects interaction design.

Scene visibility - the information of which parts of the scene are visible from a certain location—can be used to derive various properties of a virtual environment. For example, it enables the computation of viewpoint quality to determine the informativeness of a viewpoint, helps in constructing virtual tours, and allows to keep track of the objects a user may already have seen. However, computing visibility at runtime may be too computationally expensive for many applications, while sampling the entire scene beforehand introduces a costly precomputation step and may include many samples not needed later on.

Therefore, in this paper, we propose a novel approach to precompute visibility information based on navigation meshes, a polygonal representation of a scene’s navigable areas. We show that with only limited precomputation, high accuracy can be achieved in these areas. Furthermore, we demonstrate the usefulness of the approach by means of several applications, including viewpoint quality computation, landmark and room detection, and exploration assistance. In addition, we present a travel interface based on common visibility that we found to result in less cybersickness in a user study.

Viewpoint quality estimation methods allow the determination of the most informative position in a scene. However, a single position usually cannot represent an entire scene, requiring instead a set of several viewpoints. Measuring the quality of such a set of views, however, is not trivial, and the computation of an optimal set of views is an NP-hard problem.
Therefore, in this work, we propose three methods to estimate the quality of a set of views. Furthermore, we evaluate three approaches for computing an approximation to the optimal set (two of them new) regarding effectiveness and efficiency.

The manual adjustment of travel speed to cover medium or large distances in virtual environments may increase cognitive load, and manual travel at high speeds can lead to cybersickness due to inaccurate steering. In this work, we present an approach to quickly pass regions where the environment does not change much, using automated suggestions based on the computation of common visibility. In a user study, we show that our method can reduce cybersickness when compared with manual speed control.

The use of non-verbal vocal input (NVVI) as a hand-free trigger approach has proven to be valuable in previous work [Zielasko2015]. Nevertheless, BlowClick's original detection method is vulnerable to false positives and, thus, is limited in its potential use, e.g., together with acoustic feedback for the trigger. Therefore, we extend the existing approach by adding common machine learning methods. We found that a support vector machine (SVM) with Gaussian kernel performs best for detecting blowing with at least the same latency and more precision as before. Furthermore, we added acoustic feedback to the NVVI trigger, which increases the user's confidence. To evaluate the advanced trigger technique, we conducted a user study (n=33). The results confirm that it is a reliable trigger; alone and as part of a hands-free point-and-click interface.

We extended BlowClick, a NVVI metaphor for clicking, by adding machine learning methods to more reliably classify blowing events. We found a support vector machine with Gaussian kernel performing the best with at least the same latency and more precision than before. Furthermore, we added acoustic feedback to the NVVI trigger, which increases the user's confidence. With this extended technique we conducted a user study with 33 participants and could confirm that it is possible to use NVVI as a reliable trigger as part of a hands-free point-and-click interface.

In this work we describe the scenario of fully-immersive desktop VR, which serves the overall goal to seamlessly integrate with existing workflows and workplaces of data analysts and researchers, such that they can benefit from the gain in productivity when immersed in their data-spaces. Furthermore, we provide a literature review showing the status quo of techniques and methods available for realizing this scenario under the raised restrictions. Finally, we propose a concept of an analysis framework and the decisions made and the decisions still to be taken, to outline how the described scenario and the collected methods are feasible in a real use case.

Embodied, virtual agents provide users assistance in agent-based support systems. To this end, two closely linked factors have to be considered for the agents’ behavioral design: their presence time (PT), i.e., the time in which the agents are visible, and the approaching time (AT), i.e., the time span between the user’s calling for an agent and the agent’s actual availability.

This work focuses on human-like assistants that are embedded in immersive scenes but that are required only temporarily. To the best of our knowledge, guidelines for a suitable trade-off between PT and AT of these assistants do not yet exist. We address this gap by presenting the results of a controlled within-subjects study in a CAVE. While keeping a low PT so that the agent is not perceived as annoying, three strategies affecting the AT, namely fading, walking, and running, are evaluated by 40 subjects. The results indicate no clear preference for either behavior. Instead, the necessity of a better trade-off between a low AT and an agent’s realistic behavior is demonstrated.

Data from diverse workflows is often too complex for an adequate analysis without visualization. One kind of data are multi-dimensional datasets, which can be visualized via a wide array of techniques. For
instance, glyphs can be used to visualize individual datapoints. However, glyphs need to be actively looked at to be comprehended. This work explores a novel approach towards visualizing a single datapoint, with the intention of increasing the user’s awareness of it while they are looking at something else. The basic concept is to represent this point by a scene that surrounds the user in an immersive virtual environment. This idea is based on the observation that humans can extract low-detailed information, the so-called gist, from a scene nearly instantly (equal or less 100ms). We aim at providing a first step towards answering the question whether enough information can be encoded in the gist of a scene to represent a point in multi-dimensional space and if this information is helpful to the user’s understanding of this space.

It is increasingly common to embed embodied, human-like, virtual agents into immersive virtual environments for either of the two use cases: (1) populating architectural scenes as anonymous members of a crowd and (2) meeting or supporting users as individual, intelligent and conversational agents. However, the new trend towards intelligent cyber physical systems inherently combines both use cases. Thus, we argue for the necessity of multiagent systems consisting of anonymous and autonomous agents, who temporarily turn into intelligent individuals. Besides purely enlivening the scene, each agent can thus be engaged into a situation-dependent interaction by the user, e.g., into a conversation or a joint task. To this end, we devise components for an agent’s behavioral design modeling the transition between an anonymous and an individual agent when a user approaches.

Controlling user-agent-interactions by means of an external operator includes selecting the virtual interaction partners fast and faultlessly. However, especially in immersive scenes with a large
number of potential partners, this task is non-trivial.

Thus, we present a score-based recommendation system supporting an operator in the selection task. Agents are recommended as potential partners based on two parameters: the user’s distance to the agents and the user’s gazing direction. An additional graphical user interface (GUI) provides elements for configuring the system and for applying actions to those agents which the operator has confirmed as interaction partners.

Immersive visualization (IV) fosters the creation of mental images of a data set, a scene, a procedure, etc. We devise an initial version of a design space for categorizing workflows that take advantage of IV. From this categorization, specific requirements for seamlessly integrating IV can be derived. We validate the design space with three workflows emerging from our research projects.

Traditionally, experimental economics uses controlled and incentivized field and lab experiments to analyze economic behavior. However, investigating peer effects in the classic settings is challenging due to the reflection problem: Who is influencing whom?

To overcome this, we enlarge the methodological toolbox of these experiments by means of Virtual Reality. After introducing and validating a real-effort sorting task, we embed a virtual agent as peer of a human subject, who independently performs an identical sorting task. We conducted two experiments investigating (a) the subject’s productivity adjustment due to peer effects and (b) the incentive effects on competition. Our results indicate a great potential for Virtual-Reality-based economic experiments.

Common approaches for the haptic rendering of complex scenarios employ multi-rate simulation schemes. Here, the collision queries or the simulation of a complex deformable object are often performed asynchronously at a lower frequency, while some kind of intermediate contact representation is used to simulate interactions at the haptic rate. However, this can produce artifacts in the haptic rendering when the contact situation quickly changes and the intermediate representation is not able to reflect the changes due to the lower update rate.

We address this problem utilizing a novel contact model. It facilitates the creation of contact representations that are accurate for a large range of motions and multiple simulation time-steps. We handle problematic geometrically convex contact regions using a local convex decomposition and special constraints for convex areas. We combine our accurate contact model with an implicit temporal integration scheme to create an intermediate mechanical contact representation, which reflects the dynamic behavior of the simulated objects. To maintain a haptic real time simulation, the size of the region modeled by the contact representation is automatically adapted to the complexity of the geometry in contact. Moreover, we propose a new iterative solving scheme for the involved constrained dynamics problems. We increase the robustness of our method using techniques from trust region-based optimization. Our approach can be combined with standard methods for the modeling of deformable objects or constraint-based approaches for the modeling of, for instance, friction or joints. We demonstrate its benefits with respect to the simulation accuracy and the quality of the rendered haptic forces in several scenarios with one or more haptic proxies.

Abstract = {Abstract Common approaches for the haptic rendering of complex scenarios employ multi-rate simulation schemes. Here, the collision queries or the simulation of a complex deformable object are often performed asynchronously at a lower frequency, while some kind of intermediate contact representation is used to simulate interactions at the haptic rate. However, this can produce artifacts in the haptic rendering when the contact situation quickly changes and the intermediate representation is not able to reflect the changes due to the lower update rate. We address this problem utilizing a novel contact model. It facilitates the creation of contact representations that are accurate for a large range of motions and multiple simulation time-steps. We handle problematic geometrically convex contact regions using a local convex decomposition and special constraints for convex areas. We combine our accurate contact model with an implicit temporal integration scheme to create an intermediate mechanical contact representation, which reflects the dynamic behavior of the simulated objects. To maintain a haptic real time simulation, the size of the region modeled by the contact representation is automatically adapted to the complexity of the geometry in contact. Moreover, we propose a new iterative solving scheme for the involved constrained dynamics problems. We increase the robustness of our method using techniques from trust region-based optimization. Our approach can be combined with standard methods for the modeling of deformable objects or constraint-based approaches for the modeling of, for instance, friction or joints. We demonstrate its benefits with respect to the simulation accuracy and the quality of the rendered haptic forces in several scenarios with one or more haptic proxies. }, Doi = {http://dx.doi.org/10.1016/j.cag.2016.03.007}, ISSN = {0097-8493}, Keywords = {Haptic rendering}, Url = {http://www.sciencedirect.com/science/article/pii/S0097849316300206}}

Interactive analysis of 3D relational data is challenging. A common way of representing such data are node-link diagrams as they support analysts in achieving a mental model of the data. However, naïve 3D depictions of complex graphs tend to be visually cluttered, even more than in a 2D layout. This makes graph exploration and data analysis less efficient. This problem can be addressed by edge bundling. We introduce a 3D cluster-based edge bundling algorithm that is inspired by the force-directed edge bundling (FDEB) algorithm [Holten2009] and fulfills the requirements to be embedded in an interactive framework for spatial data analysis. It is parallelized and scales with the size of the graph regarding the runtime. Furthermore, it maintains the edge’s model and thus supports rendering the graph in different structural styles. We demonstrate this with a graph originating from a simulation of the function of a macaque brain.

To avoid simulator sickness and improve presence in immersive virtual environments (IVEs), high frame rates and low latency are required. In contrast, volume rendering applications typically strive for high visual quality that induces high computational load and, thus, leads to low frame rates. To evaluate this trade-off in IVEs, we conducted a controlled user study with 53 participants. Search and count tasks were performed in a CAVE with varying volume rendering conditions which are applied according to viewer position updates corresponding to head tracking. The results of our study indicate that participants preferred the rendering condition with continuous adjustment of the visual quality over an instantaneous adjustment which guaranteed for low latency and over no adjustment providing constant high visual quality but rather low frame rates. Within the continuous condition, the participants showed best task performance and felt less disturbed by effects of the visualization during movements. Our findings provide a good basis for further evaluations of how to accelerate volume rendering in IVEs according to user’s preferences.

When moving through a tracked immersive virtual environment, it is sometimes useful to deviate from the normal one-to-one mapping of real to virtual motion. One option is the application of rotation gain, where the virtual rotation of a user around the vertical axis is amplified or reduced by a factor. Previous research in head-mounted display environments has shown that rotation gain can go unnoticed to a certain extent, which is exploited in redirected walking techniques. Furthermore, it can be used to increase the effective field of regard in projection systems. However, rotation gain has never been studied in CAVE systems, yet. In this work, we present an experiment with 87 participants examining the effects of rotation gain in a CAVE-like virtual environment. The results show no significant effects of rotation gain on simulator sickness, presence, or user performance in a cognitive task, but indicate that there is a negative influence on spatial knowledge especially for inexperienced users. In secondary results, we could confirm results of previous work and demonstrate that they also hold for CAVE environments, showing a negative correlation between simulator sickness and presence, cognitive performance and spatial knowledge, a positive correlation between presence and spatial knowledge, a mitigating influence of experience with 3D applications and previous CAVE exposure on simulator sickness, and a higher incidence of simulator sickness in women.

Data annotation finds increasing use in Virtual Reality applications with the goal to support the data analysis process, such as architectural reviews. In this context, a variety of different annotation systems for application to immersive virtual environments have been presented. While many interesting interaction designs for the data annotation workflow have emerged from them, important details and evaluations are often omitted. In particular, we observe that the process of handling metadata to interactively create and manage complex annotations is often not covered in detail. In this paper, we strive to improve this situation by focusing on the design of data annotation workflows and their evaluation. We propose a workflow design that facilitates the most important annotation operations, i.e., annotation creation, review, and modification. Our workflow design is easily extensible in terms of supported annotation and metadata types as well as interaction techniques, which makes it suitable for a variety of application scenarios. To evaluate it, we have conducted a user study in a CAVE-like virtual environment in which we compared our design to two alternatives in terms of a realistic annotation creation task. Our design obtained good results in terms of task performance and user experience.

This article wants to give some impulses for a discussion about how an “ultimate” display should look like to support the Neuroscience community in an optimal way. In particular, we will have a look at immersive display technology. Since its hype in the early 90’s, immersive Virtual Reality has undoubtedly been adopted as a useful tool in a variety of application domains and has indeed proven its potential to support the process of scientific data analysis. Yet, it is still an open question whether or not such non-standard displays make sense in the context of neuroscientific data analysis. We argue that the potential of immersive displays is neither about the raw pixel count only, nor about other hardware-centric characteristics. Instead, we advocate the design of intuitive and powerful user interfaces for a direct interaction with the data, which support the multi-view paradigm in an efficient and flexible way, and – finally – provide interactive response times even for huge amounts of data and when dealing multiple datasets simultaneously.

With the increase in data availability and data volume it becomes increasingly important to extract information and actionable knowledge from data. Information Visualization helps the user to understand data by utilizing vision as a relatively parallel input channel to the user’s mind. Decision Support systems on the other hand help users in making information actionable, by suggesting beneficial decisions and presenting them in context. Both fields share a common need for understanding the interface between the computer and the human. This makes human factors research critical for both fields. Understanding limitations of human perception, cognition and action, as well as their variance must be understood to fully leverage information visualization and decision support. This article reflects on research agendas for investigating human factors in the aforementioned fields.

Proceedings of EuroVis Workshop on Reproducibility, Verification, and Validation in Visualization (EuroRV3) (2016)

Provenance tracking for visual analysis workflows is still a challenge as especially interaction and collaboration aspects are poorly covered in existing realizations. Therefore, we propose a first prototype addressing these issues based on the PROV model. Interactions in multiple applications by multiple users can be tracked by means of a web interface and, thus, allowing even for tracking of remote-located collaboration partners. In the end, we demonstrate the applicability based on two use cases and discuss some open issues not addressed by our implementation so far but that can be easily integrated into our architecture.

An immersive virtual environment is the ideal platform for the planning and training
of on-orbit servicing missions. In such kind of virtual assembly simulation, grasping
virtual objects is one of the most common and natural interactions. In this paper,
we present a novel, small and lightweight electrotactile feedback device,
specifically designed for immersive virtual environments. We conducted a study
to assess the feasibility and usability of our interaction device.
Results show that electrotactile feedback improved the user’s grasping in our virtual on-orbit servicing scenario.
The task completion time was significantly lower and the precision of the user’s interaction was higher.

Computer-controlled, human-like virtual agents (VAs), are often embedded into immersive virtual environments (IVEs) in order to enliven a scene or to assist users. Certain constraints need to be fulfilled, e.g., a collision avoidance strategy allowing users to maintain their personal space. Violating this flexible protective zone causes
discomfort in real-world situations and in IVEs. However, no studies on collision avoidance for small-scale IVEs have been conducted yet.

Our goal is to close this gap by presenting the results of a controlled user study in a CAVE. 27 participants were immersed in a small-scale office with the task of reaching the office door. Their way was blocked either by a male or female VA, representing their co-worker. The VA showed different behavioral patterns regarding gaze and locomotion.
Our results indicate that participants preferred collaborative collision avoidance: they expect the VA to step aside in order to get more space to pass while being willing to adapt their own walking paths.

Abstract = {Computer-controlled, human-like virtual agents (VAs), are often embedded into immersive virtual environments (IVEs) in order to enliven a scene or to assist users. Certain constraints need to be fulfilled, e.g., a collision avoidance strategy allowing users to maintaintheir personal space. Violating this flexible protective zone causes discomfort in real-world situations and in IVEs. However, no studies on collision avoidance for small-scale IVEs have been conducted yet. Our goal is to close this gap by presenting the results of a controlleduser study in a CAVE. 27 participants were immersed in a small-scale office with the task of reaching the office door. Theirwaywas blocked either by a male or female VA, representing their co-worker. The VA showed different behavioral patterns regarding gaze and locomotion.Our results indicate that participants preferred collaborative collision avoidance: they expect the VA to step aside in order to get more space to pass while being willing to adapt their own walking paths.}}

When traveling virtually through large scenes, long distances and different detail densities render fixed movement speeds impractical. However, to manually adjust the travel speed, users have to control an additional parameter, which may be uncomfortable and requires cognitive effort. Although automatic speed adjustment techniques exist, many of them can be problematic in indoor scenes. Therefore, we propose to automatically adjust travel speed based on viewpoint quality, originally a measure of the informativeness of a viewpoint. In a user study, we show that our technique is easy to use, allowing users to reach targets faster and use less cognitive resources than when choosing their speed manually.

Text input is an important part of the data annotation process, where text is used to capture ideas and comments. For text entry in immersive virtual environments, for which standard keyboards usually do not work, various approaches have been proposed. While these solutions have mostly proven effective, there still remain certain shortcomings making further investigations worthwhile.
Motivated by recent research, we propose the speech-based multimodal text entry system SWIFTER, which strives for simplicity while maintaining good performance. In an initial user study, we compared our approach to smartphone-based text entry within a CAVE-like virtual environment. Results indicate that SWIFTER reaches an average input rate of 23.6 words per minute and is positively received by users in terms of user experience.

To use the full potential of immersive data analysis when wearing a head-mounted display, users have to be able to navigate through the spatial data. We collected, developed and evaluated 5 different hands-free navigation methods that are usable while seated in the analyst’s usual workplace. All methods meet the requirements of being easy to learn and inexpensive to integrate into existing workplaces. We conducted a user study with 23 participants which showed that a body leaning metaphor and an accelerometer pedal metaphor performed best. In the given task the participants had to determine the shortest path between various pairs of vertices in a large 3D graph.

This paper describes a novel aircraft noise simulation technique developed at RWTH Aachen University, which makes use of aircraft noise auralization and 3D visualization to make aircraft noise both heard and seen in immersive Virtual Reality (VR) environments. This technique is intended to be used to increase the residents’ acceptance of aircraft noise by presenting noise changes in a more directly relatable form, and also aid in understanding what contributes to the residents’ subjective annoyance via psychoacoustic surveys. This paper describes the technique as well as some of its initial applications. The reasoning behind the development of such a technique is that the issue of aircraft noise experienced by residents in airport vicinities is one of subjective annoyance. Any efforts at noise abatement have been conventionally presented to residents in terms of noise level reductions in conventional metrics such as A-weighted level or equivalent sound level Leq. This conventional approach however proves insufficient in increasing aircraft noise acceptance due to two main reasons – firstly, the residents have only a rudimentary understanding of changes in decibel and secondly, the conventional metrics do not fully capture what the residents actually find annoying i.e. characteristics of aircraft noise they find least acceptable. In order to allow least resistance to air-traffic expansion, the acceptance of aircraft noise has to be increased, for which such a new approach to noise assessment is required.

Proceedings of the 22nd ACM Conference on Virtual Reality Software and Technology (VRST)

Virtual Reality (VR) has been an active field of research for several decades, with 3D interaction and 3D User Interfaces (UIs) as important sub-disciplines. However, the development of 3D interaction techniques and in particular combining several of them to construct complex and usable 3D UIs remains challenging, especially in a VR context. In addition, there is currently only limited reusable software for implementing such techniques in comparison to traditional 2D UIs. To overcome this issue, we present ViSTA Widgets, a software framework for creating 3D UIs for immersive virtual environments. It extends the ViSTA VR framework by providing functionality to create multi-device, multi-focus-strategy interaction building blocks and means to easily combine them into complex 3D UIs. This is realized by introducing a device abstraction layer along sophisticated focus management and functionality to create novel 3D interaction techniques and 3D widgets. We present the framework and illustrate its effectiveness with code and application examples accompanied by performance evaluations.

In the simulation of multi-component systems, we often encounter a problem with a lack of ground-truth data. This situation makes the validation of our simulation methods and models a difficult task. In this work we present a guideline to design validation methodologies that can be applied to the validation of multi-component simulations that lack of ground-truth data. Additionally we present an example applied to an Ultrasound Image Simulation for medical training and give an overview of the considerations made and the results for each of the validation methods. With these guidelines we expect to obtain more comparable and reproducible validation results from which other similar work can benefit.

Understanding the performance behaviour of high-performance computing (hpc) applications based on performance profiles is a challenging task. Phenomena in the performance behaviour can stem from the hpc system itself, from the application’s code, but also from the simulation domain. In order to analyse the latter phenomena, we propose a system that visualizes profile-based performance data in its spatial
context in the simulation domain, i.e., on the geometry processed by the application. It thus helps hpc experts and simulation experts understand the performance data better. Furthermore, it reduces the initially large search space by automatically labeling those parts of the data that reveal variation in performance and thus require detailed analysis.

Understanding the performance behaviour of massively parallel high-performance computing (HPC) applications based on call-path performance profiles is a time-consuming task. In this paper, we introduce the concept of directed variance in order to help analysts find performance bottlenecks in massive performance data and in the end optimize the application. According to HPC experts’ requirements, our technique automatically detects severe parts in the data that expose large variation in an application’s performance behaviour across system resources. Previously known variations are effectively filtered out. Analysts are thus guided through a reduced search space towards regions of interest for detailed examination in a 3D visualization. We demonstrate the effectiveness of our approach using performance data of common benchmark codes as well as from actively developed production codes.

LDAV 2016 – The 6th IEEE Symposium on Large Data Analysis and Visualization

Finding and understanding correlated performance behaviour of the individual functions of massively parallel high-performance computing (HPC) applications is a time-consuming task. In this poster, we propose filtered correlation analysis for automatically locating interdependencies in call-path performance profiles. Transforming the data into the frequency domain splits a performance phenomenon into sub-phenomena to be correlated separately. We provide the mathematical framework and an overview over the visualization, and we demonstrate the effectiveness of our technique.

Computer-controlled virtual humans can serve as assistants in virtual scenes. Here, they are usually in an almost constant contact with the user. Nonetheless, in some applications assistants are required only temporarily. Consequently, presenting them only when needed, i.e, minimizing their presence time, might be advisable.

To the best of our knowledge, there do not yet exist any design guidelines for such agent-based support systems. Thus, we plan to close this gap by a controlled qualitative and quantitative user study in a CAVE-like environment.We expect users to prefer assistants with a low presence time as well as a low fallback time to get quick support. However, as both factors are linked, a suitable trade-off needs to be found. Thus, we plan to test four different strategies, namely fading, moving, omnipresent and busy. This work presents our hypotheses and our planned within-subject design.

Abstract = {Computer-controlled virtual humans can serve as assistants in virtual scenes. Here, they are usually in an almost constant contact with the user. Nonetheless, in some applications assistants are required only temporarily. Consequently, presenting them only when needed, i.e., minimizing their presence time, might be advisable. To the best of our knowledge, there do not yet exist any design guidelines for such agent-based support systems. Thus, we plan to close this gap by a controlled qualitative and quantitative user study in a CAVE-like environment. We expect users to prefer assistants with a low presence time as well as a low fallback time to get quick support. However, as both factors are linked, a suitable trade-off needs to be found. Thus, we p lan to test four different strategies, namely fading, moving, omnipresent and busy. This work presents our hypotheses and our planned within-subject design.}, Booktitle = {Intelligent Virtual Agents: 16th International Conference, IVA 2016. Proceedings}, Doi = {10.1007/978-3-319-47665-0_39}, Keywords = {Virtual agent, Assistive technology, Immersive virtual environments, User study design}, Owner = {ab280112}, Timestamp = {2016.08.01}, Url = {http://dx.doi.org/10.1007/978-3-319-47665-0_39}}

In production industries, parameter identification, sensitivity analysis and multi-dimensional visualization are vital steps in the planning process for achieving optimal designs and gaining valuable information. Sensitivity analysis and visualization can help in identifying the most-influential parameters and quantify their contribution to the model output, reduce the model complexity, and enhance the understanding of the model behavior. Typically, this requires a large number of simulations, which can be both very expensive and time consuming when the simulation models are numerically complex and the number of parameter inputs increases. There are three main constituent parts in this work. The first part is to substitute the numerical, physical model by an accurate surrogate model, the so-called metamodel. The second part includes a multi-dimensional visualization approach for the visual exploration of metamodels. In the third part, the metamodel is used to provide the two global sensitivity measures: i) the Elementary Effect for screening the parameters, and ii) the variance decomposition method for calculating the Sobol indices that quantify both the main and interaction effects. The application of the proposed approach is illustrated with an industrial application with the goal of optimizing a drilling process using a Gaussian laser beam.

Proceedings of the First International Workshop on Learning Analytics Across Physical and Digital Spaces co-located with 6th International Conference on Learning Analytics & Knowledge (LAK 2016)

Interactive visual data analysis is a well-established class of methods to gather knowledge from raw and complex data. A broad variety of examples can be found in literature presenting its applicability in various ways and different scientific domains. However, fully fledged solutions for visual analysis addressing learning analytics are still rare. Therefore, this paper will discuss visual and interactive data analysis for learning analytics by presenting best practices followed by a discussion of a general architecture combining interactive visualization employing the Information Seeking Mantra in conjunction with the paradigm of coordinated multiple views. Finally, by presenting a use case for ubiquitous learning analytics its applicability will be demonstrated with the focus on temporal and spatial relation of learning data. The data is gathered from a ubiquitous learning scenario offering information for students to identify learning partners and provides information to teachers enabling the adaption of their learning material.

Abstract = {Interactive visual data analysis is a well-established class of methods to gather knowledge from raw and complex data. A broad variety of examples can be found in literature presenting its applicability in various ways and different scientific domains. However, fully fledged solutions for visual analysis addressing learning analytics are still rare. Therefore, this paper will discuss visual and interactive data analysis for learning analytics by presenting best practices followed by a discussion of a general architecture combining interactive visualization employing the Information Seeking Mantra in conjunction with the paradigm of coordinated multiple views. Finally, by presenting a use case for ubiquitous learning analytics its applicability will be demonstrated with the focus on temporal and spatial relation of learning data. The data is gathered from a ubiquitous learning scenario offering informationfor students to identify learning partners and provides information to teachers enabling the adaption of their learning material.}, Keywords = {interactive analysis, web-based visualization, learning analytics}, Url = {http://ceur-ws.org/Vol-1601/}}

To use the full potential of immersive data analysis when wearing a head-mounted display, the user has to be able to navigate through the spatial data. We collected, developed and evaluated 5 different hands-free navigation methods that are usable while seated in the analyst’s usual workplace. All methods meet the requirements of being easy to learn and inexpensive to integrate into existing workplaces. We conducted a user study with 23 participants which showed that a body leaning metaphor and an accelerometer pedal metaphor performed best within the given task.

Orientation and wayfinding in architectural Immersive Virtual Environments (IVEs) are non-trivial, accompanying tasks which generally support the users’ main task. World in Miniatures (WIMs)— essentially 3D maps containing a scene replica—are an established approach to gain survey knowledge about the virtual world, as well as information about the user’s relation to it. However, for largescale, information-rich scenes, scaling and occlusion issues result in diminishing returns. Since there typically is a lack of standardized information regarding scene decompositions, presenting the inside of self-contained scene extracts is challenging.

Therefore, we present an automatic WIM generation workflow for arbitrary, realistic in- and outdoor IVEs in order to support users with meaningfully selected and scaled extracts of the IVE as well as corresponding context information. Additionally, a 3D user interface is provided to manually manipulate the represented extract.

Abstract = {Orientation and wayfinding in architectural Immersive Virtual Environments (IVEs) are non-trivial, accompanying tasks which generally support the users’ main task. World in Miniatures (WIMs)—essentially 3D maps containing a scene replica—are an established approach to gain survey knowledge about the virtual world, as well as information about the user’s relation to it. However, for largescale, information-rich scenes, scaling and occlusion issues result in diminishing returns. Since there typically is a lack of standardized information regarding scene decompositions, presenting the inside of self-contained scene extracts is challenging. Therefore, we present an automatic WIM generation workflow for arbitrary, realistic in- and outdoor IVEs in order to support users with meaningfully selected and scaled extracts of the IVE as well as corresponding context information. Additionally, a 3D user interface is provided to manually manipulate the represented extract.}}

LDAV 2016 – The 6th IEEE Symposium on Large Data Analysis and Visualization

We present an approach for tracking space-filling features based on a two-step algorithm utilizing two graph optimization techniques. First, one-to-one assignments between successive time steps are found by a matching on a weighted, bi-partite graph. Second, events are detected by computing an independent set on potential event explanations. The main objective of this work is investigating options for formal evaluation of complex feature tracking algorithms in the absence of ground truth data.

@INPROCEEDINGS{Schnorr2016, author = {Andrea Schnorr and Sebastian Freitag and Dirk Helmrich and Torsten W. Kuhlen and Bernd Hentschel}, title = {{F}ormal {E}valuation {S}trategies for {F}eature {T}racking}, booktitle = Proc # { the } # LDAV, year = {2016}, pages = {103--104}, abstract = { We present an approach for tracking space-filling features based on a two-step algorithm utilizing two graph optimization techniques. First, one-to-one assignments between successive time steps are found by a matching on a weighted, bi-partite graph. Second, events are detected by computing an independent set on potential event explanations. The main objective of this work is investigating options for formal evaluation of complex feature tracking algorithms in the absence of ground truth data.}, doi = { 10.1109/LDAV.2016.7874339}}

Phenomena in the performance behaviour of high-performance computing (HPC) applications can stem from the HPC system itself, from the application's code, but also from the simulation domain. In order to analyse the latter phenomena, we propose a system that visualizes profile-based performance data in its spatial context, i.e., on the geometry, in the simulation domain. It thus helps HPC experts but also simulation experts understand the performance data better. In addition, our tool reduces the initially large search space by automatically labelling large-variation views on the data which require detailed analysis.

We present a novel approach for tracking space-filling features, i.e., a set of features covering the entire domain. The assignment between successive time steps is determined by a two-step, global optimization scheme. First, a maximum-weight, maximal matching on a bi-partite graph is computed to provide one-to-one assignments between features of successive time steps. Second, events are detected in a subsequent step; here the matching step serves to restrict the exponentially large set of potential solutions. To this end, we compute an independent set on a graph representing conflicting event explanations. The method is evaluated by tracking dissipation elements, a structure definition from turbulent flow analysis.

Virtual Environments: Current Topics in Psychological Research (VECTOR) workshop, 2016

Virtual Agents (VAs) are embedded in virtual environments for two reasons: they enliven architectural scenes by representing more realistic situations, and they are dialogue partners. They can function as training partners such as representing students in a teaching scenario, or as assistants by, e.g., guiding users through a scene or by performing certain tasks either individually or in collaboration with the user. However, designing such VAs is challenging as various requirements have to be met. Two relevant factors will be briefly discussed in the talk: Collision Avoidance and Presence Strategies.

Modeling large-scale spiking neural networks showing realistic biological behavior in their dynamics is a complex and tedious task. Since these networks consist of millions of interconnected neurons, their simulation produces an immense amount of data. In recent years it has become possible to simulate even larger networks. However, solutions to assist researchers in understanding the simulation's complex emergent behavior by means of visualization are still lacking. While developing tools to partially fill this gap, we encountered the challenge to integrate these tools easily into the neuroscientists' daily workflow. To understand what makes this so challenging, we looked into the workflows of our collaborators and analyzed how they use the visualizations to solve their daily problems. We identified two major issues: first, the analysis process can rapidly change focus which requires to switch the visualization tool that assists in the current problem domain. Second, because of the heterogeneous data that results from simulations, researchers want to relate data to investigate these effectively. Since a monolithic application model, processing and visualizing all data modalities and reflecting all combinations of possible workflows in a holistic way, is most likely impossible to develop and to maintain, a software architecture that offers specialized visualization tools that run simultaneously and can be linked together to reflect the current workflow, is a more feasible approach. To this end, we have developed a software architecture that allows neuroscientists to integrate visualization tools more closely into the modeling tasks. In addition, it forms the basis for semantic linking of different visualizations to reflect the current workflow. In this paper, we present this architecture and substantiate the usefulness of our approach by common use cases we encountered in our collaborative work.

Modal sound synthesis is a promising approach for real-time physically-based sound synthesis. A modal analysis is used to compute characteristic vibration modes from the geometry and material properties of scene objects. These modes allow an efficient sound synthesis at run-time, but the analysis is computationally expensive and thus typically computed in a pre-processing step. In interactive applications, however, objects may be created or modified at run-time. Unless the new shapes are known upfront, the modal data cannot be pre-computed and thus a modal analysis has to be performed at run-time. In this paper, we present a system to compute modal sound data at run-time for interactive applications. We evaluate the computational requirements of the modal analysis to determine the computation time for objects of different complexity. Based on these limits, we propose using different levels-of-detail for the modal analysis, using different geometric approximations that trade speed for accuracy, and evaluate the errors introduced by lower-resolution results. Additionally, we present an asynchronous architecture to distribute and prioritize modal analysis computations.

Common approaches for the haptic rendering of complex scenarios employ multi-rate simulation schemes. Here, the collision queries or the simulation of a complex deformable object are often performed asynchronously on a lower frequency, while some kind of intermediate contact representation is used to simulate interactions on the haptic rate. However, this can produce artifacts in the haptic rendering when the contact situation quickly changes and the intermediate representation is not able to reflect the changes due to the lower update rate. We address this problem utilizing a novel contact model. It facilitates the creation of contact representations that are accurate for a large range of motions and multiple simulation time-steps.We handle problematic convex contact regions using a local convex decomposition and special constraints for convex areas.We combine our accurate contact model with an implicit temporal integration scheme to create an intermediate mechanical contact representation, which reflects the dynamic behavior of the simulated objects. Moreover, we propose a new iterative solving scheme for the involved constrained dynamics problems.We increase the robustness of our method using techniques from trust region-based optimization. Our approach can be combined with standard methods for the modeling of deformable objects or constraint-based approaches for the modeling of, for instance, friction or joints. We demonstrate its benefits with respect to the simulation accuracy and the quality of the rendered haptic forces in multiple scenarios.

In this work we present a haptic training simulator for a maxillofacial procedure comprising the controlled breaking of the lower mandible. To our knowledge the haptic simulation of fracture is seldom addressed, especially when a realistic breaking behavior is required. Our system combines bimanual haptic interaction with a simulation of the bone based on well-founded methods from fracture mechanics. The system resolves the conflict between simulation complexity and haptic real-time constraints by employing a dedicated multi-rate simulation and a special solving strategy for the occurring mechanical equations. Furthermore, we present remeshing-free methods for collision
detection and visualization which are tailored for an efficient treatment of the topological changes induced by the fracture. The methods have been successfully implemented and tested in a simulator prototype using real pathological data and a semi-immersive VR-system with two haptic devices. We evaluated the computational efficiency of our methods and show that a stable and responsive haptic simulation of the fracturing has been achieved.

In Proc. of the IEEE Conference on Virtual Reality SEARIS Workshop. (2015)

The act of note-taking is an essential part of the data analysis process. It has been realized in form of various annotation systems that have been discussed in many publications. Unfortunately, the focus usually lies on high-level functionality, like interaction metaphors and display strategies. We argue that it is worthwhile to also consider software engineering aspects. Annotation systems often share similar functionality that can potentially be factored into reusable components with the goal to speed up the creation of new annotation systems. At the same time, however, VR-centered annotation systems are not only subject to application-specific requirements, but also to those arising from differences between the various VR platforms, like desktop VR setups or CAVEs. As a result, it is usually necessary to build application-specific VR-centered annotation systems from scratch instead of reusing existing components.

To improve this situation, we present a framework that provides reusable and adaptable building blocks to facilitate the creation of flexible annotation systems for VR applications. We discuss aspects ranging from data representation over persistence to the integration of new data types and interaction metaphors, especially in context of multi-platform applications. To underpin the benefits of such an approach and promote the proposed concepts, we describe how the framework was applied to several of our own projects.

Eurographics Workshop on Visual Computing for Biology and Medicine (2015)

When learning ultrasound (US) imaging, trainees must learn how to recognize structures, interpret textures and shapes, and simultaneously register the 2D ultrasound images to their 3D anatomical mental models. Alleviating the cognitive load imposed by these tasks should free the cognitive resources and thereby improve the learning process. We argue that the amount of cognitive load that is required to mentally rotate the models to match the images to them is too large and therefore negatively impacts the learning process. We present a 3D visualization tool that allows the user to naturally move a 2D slice and navigate around a 3D anatomical model. The slice is displayed in-place to facilitate the registration of the 2D slice in its 3D context. Two duplicates are also shown externally to the model; the first is a simple rendered image showing the outlines of the structures and the second is a simulated ultrasound image. Haptic cues are also provided to the users to help them maneuver around the 3D model in the virtual space. With the additional display of annotations and information of the most important structures, the tool is expected to complement the available didactic material used in the training of ultrasound procedures.

Proceedings of the 25th International Conference on Artificial Reality and Telexistence and the 20th Eurographics Symposium on Virtual Environments (ICAT-EGVE), 2015

The knowledge of which places in a virtual environment are interesting or informative can be used to improve user interfaces and to create virtual tours. Viewpoint Quality Estimation algorithms approximate this information by calculating quality scores for viewpoints. However, even though several such algorithms exist and have also been used, e.g., in virtual tour generation, they have never been comparatively evaluated on virtual scenes.
In this work, we introduce three new Viewpoint Quality Estimation algorithms, and compare them against each other and six existing metrics, by applying them to two different virtual scenes. Furthermore, we conducted a user study to obtain a quantitative evaluation of viewpoint quality. The results reveal strengths and limitations of the metrics on actual scenes, and provide recommendations on which algorithms to use for real applications.

In this work, we present an approach for tracking the feet of multiple users in CAVE-like systems with under-floor projection. It is based on low-cost consumer cameras, does not require users to wear additional equipment, and can be installed without modifying existing components. If the brightness of the floor projection does not contain too much variation, the feet of several people can be successfully and precisely tracked and assigned to individuals. The tracking data can be used to enable or enhance user interfaces like Walking-in-Place or torso-directed steering, provide audio feedback for footsteps, and improve the immersive experience for multiple users.

In contrast to the wide-spread use of 6-DOF pointing devices, freehand user interfaces in Immersive Virtual Environments (IVE) are non-intrusive. However, for gesture interfaces, the definition of trigger signals is challenging. The use of mechanical devices, dedicated trigger gestures, or speech recognition are often used options, but each comes with its own drawbacks. In this paper, we present an alternative approach, which allows to precisely trigger events with a low latency using microphone input. In contrast to speech recognition, the user only blows into the microphone. The audio signature of such blow events can be recognized quickly and precisely. The results of a user study show that the proposed method allows to successfully complete a standard selection task and performs better than expected against a standard interaction device, the Flystick.

Making music by blowing on bottles is fun but challenging. We introduce a novel 3D user interface to play songs on virtual bottles. For this purpose the user blows into a microphone and the stream of air is recreated in the virtual environment and redirected to virtual bottles she is pointing to with her fingers. This is easy to learn and subsequently opens up opportunities for quickly switching between bottles and playing groups of them together to form complex
melodies. Furthermore, our interface enables the customization of the virtual environment, by means of moving bottles, changing their type or filling level.

The advection of integral lines is an important computational kernel in vector field visualization. We investigate how this kernel can profit from vector (SIMD) extensions in modern CPUs. As a baseline, we formulate a streamline tracing algorithm that facilitates auto-vectorization by an optimizing compiler. We analyze this algorithm and propose two different optimizations. Our results show that particle tracing does not per se benefit from SIMD computation. Based on a careful analysis of the auto-vectorized code, we propose an optimized data access routine and a re-packing scheme which increases average SIMD efficiency. We evaluate our approach on three different, turbulent flow fields. Our optimized approaches increase integration performance up to 5:6 over our baseline measurement. We conclude with a discussion of current limitations and aspects for future work.

@INPROCEEDINGS{Hentschel2015, author = {Bernd Hentschel and Jens Henrik G{\"o}bbert and Michael Klemm andPaul Springer and Andrea Schnorr and Torsten W. Kuhlen}, title = {{P}acket-{O}riented {S}treamline {T}racing on {M}odern {SIMD}{A}rchitectures}, booktitle = {Proceedings of the Eurographics Symposium on Parallel Graphicsand Visualization}, year = {2015}, pages = {43--52}, abstract = {The advection of integral lines is an important computationalkernel in vector field visualization. We investigatehow this kernel can profit from vector (SIMD) extensions in modern CPUs. As abaseline, we formulate a streamlinetracing algorithm that facilitates auto-vectorization by an optimizing compiler.We analyze this algorithm andpropose two different optimizations. Our results show that particle tracing doesnot per se benefit from SIMD computation.Based on a careful analysis of the auto-vectorized code, we propose an optimizeddata access routineand a re-packing scheme which increases average SIMD efficiency. We evaluate ourapproach on three different,turbulent flow fields. Our optimized approaches increase integration performanceup to 5.6x over our baselinemeasurement. We conclude with a discussion of current limitations and aspectsfor future work.}}

Proceedings of 21st International Conference on Collaboration and Technology (CRIWG) (2015)

Various conceptual approaches for the creation and presentation of virtual museums can be found. However, less work exists that concentrates on collaboration in virtual museums. The support of collaboration in virtual museums provides various benefits for the visit as well as the preparation and creation of virtual exhibits. This paper addresses one major problem of collaboration in virtual museums: the awareness of visitors. We use a Cave Automated Virtual Environment (CAVE) for the visualization of generated virtual museums to offer simple awareness through co-location. Furthermore, the use of smartphones during the visit enables the visitors to create comments or to access exhibit related metadata. Thus, the main contribution of this ongoing work is the presentation of a workflow that enables an integrated deployment of generic virtual museums into a CAVE, which will be demonstrated by deploying the virtual Leopold Fleischhacker Museum.

Metadata in- and output are important steps within the data annotation process. However, selecting techniques that effectively facilitate these steps is non-trivial, especially for applications that have to run on multiple virtual reality platforms. Not all techniques are applicable to or available on every system, requiring to adapt workflows on a per-system basis. Here, we describe a metadata handling system based on Android's Intent system that automatically adapts workflows and thereby makes manual adaption needless.

In this work, we present an approach for tracking the feet of mul- tiple users in CAVE-like systems with under-floor projection. It is based on low-cost consumer cameras, does not require users to wear additional equipment, and can be installed without modifying existing components. If the brightness of the floor projection does not contain too much variation, the feet of several people can be reliably tracked and assigned to individuals.

In this work, we report on a pilot study we conducted, and on a study design, to examine the effects and applicability of rotation gain in CAVE-like virtual environments. The results of the study will give recommendations for the maximum levels of rotation gain that are reasonable in algorithms for enlarging the virtual field of regard or redirected walking.

Virtual Reality (VR) systems are of growing importance to aid decision support in the context of the digital factory, especially factory layout planning. While current solutions either focus on virtual walkthroughs or the visualization of more abstract information, a solution that provides both, does currently not exist. To close this gap, we present a holistic VR application, called Factory Layout Planning Assistant (flapAssist). It is meant to serve as a platform for planning the layout of factories, while also providing a wide range of analysis features. By being scalable from desktops to CAVEs and providing a link to a central integration platform, flapAssist integrates well in established factory planning workflows.

We present a novel approach for tracking space-filling features, i.e. a set of features which covers the entire domain. In contrast to previous work, we determine the assignment between features from successive time steps by computing a globally optimal, maximum-weight, maximal matching on a weighted, bi-partite graph. We demonstrate the method's functionality by tracking dissipation elements (DEs), a space-filling structure definition from turbulent flow analysis. The ability to track DEs over time enables researchers from fluid mechanics to extend their analysis beyond the assessment of static flow fields to time-dependent settings.

Factory planning is a highly heterogeneous process that involves various expert groups at the same time. In this context, the communication between different expert groups poses a major challenge. One reason for this lies in the differing domain knowledge of individual groups. However, since decisions made within one domain usually have an effect on others, it is essential to make these domain interactions visible to all involved experts in order to improve the overall planning process.
In this paper, we present a concept that facilitates the integration of two separate virtual-reality- and visualization analysis tools for different application domains of the planning process. The concept was developed in context of the Virtual Production Intelligence and aims at creating an approach to making domain interactions visible, such that the aforementioned challenges can be mitigated.

The integration of independent applications is a complex task from a software engineering perspective. Nonetheless, it entails significant benefits, especially in the context of Virtual Reality (VR) supported factory planning, e.g., to communicate interdependencies between different domains. To emphasize this aspect, we integrated two independent VR and visualization applications into a holistic planning solution. Special focus was put on parallelization and interaction aspects, while also considering more general requirements of such an integration process. In summary, we present technical solutions for the effective integration of several VR applications into a holistic solution with the integration of two applications from the context of factory planning with special focus on parallelism and interaction aspects. The effectiveness of the approach is demonstrated by performance measurements.

Digital works of art are often created using some kind of modeling software, like Cinema4D. Usually they are presented in a non-interactive form, like large Diasecs, and can thus only be experienced by passive viewing. To explore alternative, more captivating presentation channels, we investigate the use of a CAVE virtual reality (VR) system as an immersive and interactive presentation platform in this paper. To this end, in a collaboration with an artist, we built an interactive VR experience from one of his existing works. We provide details on our design and report on the results of a qualitative user study.

Modal sound synthesis is a useful method to interactively generate sounds for Virtual Environments. Forces acting on objects excite modes, which then have to be accumulated to generate the output sound. Due to the high audio sampling rate, algorithms using the CPU typically can handle only a few actively sounding objects. Additionally, force excitation should be applied at a high sampling rate. We present different algorithms to compute the synthesized sound using a GPU, and compare them to CPU implementations. The GPU algorithms shows a significantly higher performance, and allows many sounding objects simultaneously.

More than two decades have passed since the introduction of the CAVE (Cave Automatic Virtual Environment), a landmark in the development of VR.1 The CAVE addressed two major issues with head-mounted displays of the era. First, it provided an unprecedented field of view, greatly improving the Feeling of presence in a virtual environment (VE). Second, this feeling was ampli ed because users didn’t have to rely on a virtual representation of their own bodies or parts thereof. Instead, they could physically enter the virtual space. Scientific visualization had been promulgated as a killer app for VR technology almost from day one. With the CAVE’s inception, it became possible to “put users within their data.” Proponents predicted two key advantages. First, immersive VR promised faster, more comprehensive understanding of complex, spatial relationships owing to head-tracked, stereoscopic rendering. Second, it would provide a more natural user interface, specifically for spatial interaction. In a seminal article, Andy van Dam and his colleagues proposed VR-enabled visualization as a midterm solution to the “accelerating data crisis.”2 That is, the ability to generate data had for some time outpaced the ability to analyze it. Over the years, a number of studies have investigated the effects of VR-based visualizations in speci c application scenarios. Recently, Bireswar Laha and his colleagues provided
more general, empirical evidence for its benefits.
Although VR and scienti c visualization have matured and many of the original technical limitations have been resolved, immersive visualization has yet to nd the widespread, everyday use
that was claimed in the early days. At the same time, the demand for scalable visualization solutions
is greater than ever. If anything, the gap between data generation and analysis capabilities has widened even more. So, two questions arise. What should such scalable solutions look like, and what requirements arise regarding the underlying hardware and software and the overall
methodology?

Successful bone sawing requires a high level of skill and experience, which could be gained by the use of Virtual Reality-based simulators. A key aspect of these medical simulators is realistic force feedback.
The aim of this paper is to model the bone sawing process in order to develop a valid training simulator for the bilateral sagittal split osteotomy, the most often applied corrective surgery in case of a malposition of the mandible. Bone samples from a human cadaveric mandible were tested using a designed experimental system. Image processing and statistical analysis were used for the selection of four models for the bone sawing process. The results revealed a polynomial dependency between the material removal rate and the applied force. Differences between the three segments of the osteotomy line and between the cortical and cancellous bone were highlighted.

Real walking is the most natural method of navigation in virtual environments. However, physical space limitations often prevent or complicate its continuous use. Thus, many real walking interfaces, among them redirected walking techniques, depend on a reorientation technique that redirects the user away from physical boundaries when they are reached. However, existing reorientation techniques typically actively interrupt the user, or depend on the application of rotation gain that can lead to simulator sickness. In our approach, the user is reoriented using portals. While one portal is placed automatically to guide the user to a safe position, she controls the target selection and physically walks through the portal herself to perform the reorientation. In a formal user study we show that the method does not cause additional simulator sickness, and participants walk more than with point-and-fly navigation or teleportation, at the expense of longer completion times.

Recently, more and more Virtual Reality (VR) and visualization solutions to support the factory layout planning process have been presented. On the one hand, VR enables planners to create cost-effective virtual prototypes and to perform virtual walkthroughs, e.g., to verify proposed layouts. On the other hand, visualization helps to gain insight into simulation results that, e.g., describe the various interdependencies between machines, such as material flows. In order to create truly effective tools based on VR and visualization, the right techniques have to be chosen and adapted to the specific problem. However, the solutions published so far usually do not exploit these technologies to their full potential.
To address this situation, we present a VR-based planning assistant that offers advanced visualization functionality that furthers the understanding of planning-relevant parameters, while also relying on established techniques. In order to realize a useful approach, the assistant fulfills three central requirements:

A smooth integration of the assistant into existing workflows is essential in order to not disrupt them. Consequently, existing tools need to be properly integrated and a mechanism for data exchange with these tools has to be provided.

Visualization is the main means of facilitating insight. Instead of only displaying factory models, advanced techniques to visualize more abstract quantities, like material flows or process chains, have to be provided.

VR systems vary in the degree of immersion they offer, ranging from non-immersive desktop systems to fully immersive Cave Automatic Virtual Environment (CAVE) systems. Scalability among these systems allows adapting high-end installations as well as cost-effective solutions. However, to ensure good scalability, devising a flexible system abstraction and a unified interaction concept are essential.

The purpose of this paper is twofold. First, our VR-based planning assistant is introduced and realization details are presented. Second, by presenting technical details of the used techniques we aim at providing VR and visualization guidelines for the creation or extension of VR-based factory layout planning tools.
The base for our planning assistant is an immersive VR (IVR) system in form of a CAVE. Our solution allows performing virtual walkthroughs and offers additional visualization techniques for planning relevant data.

In the recent past, efforts have been made to adopt immersive virtual reality (IVR) systems as a means for design reviews in factory layout planning. While several solutions for this scenario have been developed, their integration into existing planning workflows has not been discussed yet. From our own experience of developing such a solution, we conclude that the use of IVR systems-like CAVEs-is rather disruptive to existing workflows. One major reason for this is that IVR systems are not available everywhere due to their high costs and large physical footprint. As a consequence, planners have to travel to sites offering such systems which is especially prohibitive as planners are usually geographically dispersed. In this paper, we present a concept for integrating IVR systems into the factory planning process by means of a 3D collaborative virtual environment (3DCVE) without disrupting the underlying planning workflow. The goal is to combine non-immersive and IVR systems to facilitate collaborative walkthrough sessions. However, this scenario poses unique challenges to interactive collaborative work that to the best of our knowledge have not been addressed so far. In this regard, we discuss approaches to viewpoint sharing, telepointing and annotation support that are geared towards distributed heterogeneous 3DCVEs.

In this paper a single-point haptic rendering technique is proposed which uses a constraint-based physics simulation approach.
Geometries are sampled using point shell points, each associated with a small disk, that jointly result in a closed surface for the whole shell.
The geometric information is incorporated into the constraint-based simulation using newly introduced geometrically limited contact constraints
which are active in a restricted region corresponding to the disks in contact.
The usage of disk constraints not only creates closed surfaces, which is important for single-point rendering,
but also tackles the problem of over-constraint contact situations in convex geometric setups.
Furthermore, an iterative solving scheme for dynamic problems under consideration of the proposed constraint type is proposed.
Finally, an evaluation of the simulation approach shows the advantages compared to standard contact constraints regarding the quality of the rendered forces.

This paper presents a software framework that supports the development of haptic-enabled physics simulations.
The framework provides tools aiming to facilitate a fast prototyping process by utilizing component and flow-oriented architectures,
while maintaining the capability to create efficient code which fulfills the performance requirements induced by the target applications.
We argue that such a framework should not only ease the creation of prototypes but also help to effectively and efficiently evaluate them.
To this end, we provide analysis tools and the possibility to build problem oriented evaluation environments based on the described software concepts.
As motivating use case, we present a project with the goal to develop a haptic-enabled medical training simulator for a maxillofacial procedure. With this example, we demonstrate how the described framework can be used to create a simulation architecture for a complex haptic simulation and how the tools assist in the prototyping process.

System control is a crucial task for many virtual reality applications and can be realized in a broad variety of ways, whereat the most common way is the use of graphical menus. These are often implemented as part of the virtual environment, but can also be displayed on mobile devices. Until now, many systems and studies have been published on using mobile devices such as personal digital assistants (PDAs) to realize such menu systems. However, most of these systems have been proposed way before smartphones existed and evolved to everyday companions for many people. Thus, it is worthwhile to evaluate the applicability of modern smartphones as carrier of menu systems for immersive virtual environments. To do so, we implemented a platform-independent menu system for smartphones and evaluated it in two different ways. First, we performed an expert review in order to identify potential design flaws and to test the applicability of the approach for demonstrations of VR applications from a demonstrator's point of view. Second, we conducted a user study with 21 participants to test user acceptance of the menu system. The results of the two studies were contradictory: while experts appreciated the system very much, user acceptance was lower than expected. From these results we could draw conclusions on how smartphones should be used to realize system control in virtual environments and we could identify connecting factors for future research on the topic.

Recently, virtual reality (VR) and visualization have been increasingly employed to facilitate various tasks in factory planning processes. One major challenge in this context lies in the exchange of information between expert groups concerned with distinct planning tasks in order to make planners aware of inter-dependencies. For example, changes to the configuration of individual machines can have an effect on the overall production performance and vice versa. To this end, we developed VR- and visualization-based planning tools for two distinct planning tasks for which we present an integration concept that facilitates information exchange between these tools. The first application's goal is to facilitate layout planning by means of a CAVE system. The high degree of immersion offered by this system allows users to judge spatial relations in entire factories through cost-effective virtual walkthroughs. Additionally, information like material flow data can be visualized within the virtual environment to further assist planners to comprehensively evaluate the factory layout.
Another application focuses on individual machines with the goal to help planners find ideal configurations by providing a visualization solution to explore the multi-dimensional parameter space of a single machine. This is made possible through the use of meta-models of the parameter space that are then visualized by means of the concept of Hyperslice.
In this paper we present a concept that shows how these applications can be integrated into one comprehensive planning tool that allows for planning factories while considering factors of different planning levels at the same time. The concept is backed by Virtual Production Intelligence (VPI), which integrates data from different levels of factory processes, while including additional data sources and algorithms to provide further information to be used by the applications.
In conclusion, we present an integration concept for VR- and visualization-based software tools that facilitates the communication of interdependencies between different factory planning tasks. As the first steps towards creating a comprehensive factory planning solution, we demonstrate the integration of the aforementioned two use-cases by applying VPI. Finally, we review the proposed concept by discussing its benefits and pointing out potential implementation pitfalls.

Four new structures based on CaCl2 and proline are reported, all with an unusual Cl–Ca–Cl moiety. Depending on the stoichiometry and the chirality of the amino acid, this metal dihalide fragment represents the core of a mononuclear Ca complex or may be linked by the carboxylate to form extended structures. A cisoid coordination of the halide atoms at the calcium cation is encountered in a chain polymer. In the 2D structures, CaCl2 dumbbells act as nodes and are crosslinked by either enantiomerically pure or racemic proline to form square lattice nets. Extensive database searches and topology tests prove that this structure type is rare for MCl2 dumbbells in general and unprecedented for Ca compounds.Four new structures based on CaCl2 and proline are reported, all with an unusual Cl–Ca–Cl moiety. Depending on the stoichiometry and the chirality of the amino acid, this metal dihalide fragment represents the core of a mononuclear Ca complex or may be linked by the carboxylate to form extended structures. A cisoid coordination of the halide atoms at the calcium cation is encountered in a chain polymer. In the 2D structures, CaCl2 dumbbells act as nodes and are crosslinked by either enantiomerically pure or racemic proline to form square lattice nets. Extensive database searches and topology tests prove that this structure type is rare for MCl2 dumbbells in general and unprecedented for Ca compounds.

The Human Brain Project is one of the largest scientific initiatives dedicated to the research of the human brain worldwide. Over 80 research groups from a broad variety of scientific areas, such as neuroscience, simulation science, high performance computing, robotics, and visualization work together in this European research initiative. This work at hand will identify certain chances and challenges for cognitive systems engineering resulting from the HBP research activities. Beside the main goal of the HBP gathering deeper insights into the structure and function of the human brain, cognitive system research can directly benefit from the creation of cognitive architectures, the simulation of neural networks, and the application of these in context of (neuro-)robotics. Nevertheless, challenges arise regarding the utilization and transformation of these research results for cognitive systems, which will be discussed in this paper. Tools necessary to cope with these challenges are visualization techniques helping to understand and gain insights into complex data. Therefore, this paper presents a set of visualization techniques developed at the Virtual Reality Group at the RWTH Aachen University.

IEEE VIS International Workshop on 3DVis: Does 3D really make sense for Data Visualization (2014)

Immersive virtual environments (IVEs) are an appropriate platform for 3D data visualization and exploration as, for example, the spatial understanding of these data is facilitated by stereo technology. However, in comparison to desktop setups a lower latency and thus a higher frame rate is mandatory. In this paper we argue that current realizations of direct volume rendering do not allow for a desirable visualization w.r.t. latency and visual quality that do not impair the immersion in virtual environments. To this end, we analyze published acceleration techniques and discuss their potential in IVEs; furthermore, head tracking is considered as a main challenge but also a starting point for specific optimization techniques.

Proceedings of the First Workshop on Visual Performance Analysis (2014)

The available memory bandwidth of existing high performance computing platforms turns out as being more and more the limitation to various applications. Therefore, modern microarchitectures integrate the memory controller on the processor chip, which leads to a non-uniform memory access behavior of such systems. This access behavior in turn entails major challenges in the development of shared memory parallel applications. An improperly implemented memory access functionality results in a bad ratio between local and remote memory access, and causes low performance on such architectures. To address this problem, the developers of such applications rely on tools to make these kinds of performance problems visible. This work presents a new tool for the visualization of performance data of the non-uniform memory access behavior. Because of the visual design of the tool, the developer is able to judge the severity of remote memory access in a time-dependent simulation, which is currently not possible using existing tools.

Simulations of geothermal reservoirs inherently contain uncertainty due to the fact that the underlying physical models are created from sparse data. Moreover, this uncertainty often cannot be completely expressed by simple key measures (e.g., mean and standard deviation), as the distribution of possible values is often not unimodal. Nevertheless, existing visualizations of these simulation data often completely neglect displaying the uncertainty, or are limited to a mean/variance representation. We present an approach to visualize geothermal simulation data that deals with both cases: scalar uncertainties as well as general ensembles of data sets. Users can interactively define two-dimensional transfer functions to visualize data and uncertainty values directly, or browse a 2D scatter plot representation to explore different possibilities in an ensemble.

Guided tours have been found to be a good approach to introducing users to previously unknown virtual environments and to allowing them access to relevant points of interest. Two important tasks during the creation of guided tours are the definition of views onto relevant information and their arrangement into an order in which they are to be visited. To allow a maximum of flexibility an interactive approach to these tasks is desirable. To this end, we present and evaluate two approaches to the mentioned interaction tasks in this paper. The first approach is a hybrid 2D/3D interaction metaphor in which a tracked tablet PC is used as a virtual digital camera that allows to specify and order views onto the scene. The second one is a purely 3D version of the first one, which does not require a tablet PC. Both approaches were compared in an initial user study, whose results indicate a superiority of the 3D over the hybrid approach.

Graphs play an important role in data analysis. Especially, graphs with a natural spatial embedding can benefit from a 3D visualization. But even more then in 2D, graphs visualized as intuitively readable 3D node-link diagrams can become very cluttered. This makes graph exploration and data analysis difficult. For this reason, we focus on the challenge of reducing edge clutter by utilizing edge bundling. In this paper we introduce a parallel, edge cluster
based accelerator for the force-directed edge bundling algorithm presented in [Holten2009]. This opens up the possibility for user interaction during and after both the clustering and the bundling.

The visual discrimination of different structures in one or multiple combined volume data sets is generally done with individual transfer functions that can usually be adapted interactively. Immersive virtual environments support the depth perception and thus the spatial orientation in these volume visualizations. However, complex 2D menus for elaborate transfer function design cannot be easily integrated. We therefore present an approach for changing the color mapping during volume exploration with direct volume interaction and an additional 3D widget. In this way we incorporate the modification of a color mapping for a large number of discretely labeled brain areas in an intuitive way into the virtual environment. We use our approach for the analysis of a patient’s data with a brain tissue degenerating disease to allow for an interactive analysis of affected regions.

Computer-assisted processing and interpretation of medical ultrasound images is one of the most challenging tasks within image analysis. Physical phenomena in ultrasonographic images, e.g., the characteristic speckle noise and shadowing effects, make the majority of standard methods from image analysis non optimal. Furthermore, validation of adapted computer vision methods proves to be difficult due to missing ground truth information. There is no widely accepted software phantom in the community and existing software phantoms are not flexible enough to support the use of specific speckle models for different tissue types, e.g., muscle and fat tissue. In this work we propose an anatomical software phantom with a realistic speckle pattern simulation to fill this gap and provide a flexible tool for validation purposes in medical ultrasound image analysis. We discuss the generation of speckle patterns and perform statistical analysis of the simulated textures to obtain quantitative measures of the realism and accuracy regarding the resulting textures.

The visualization of the progression of brain tissue loss in neurodegenerative diseases like corticobasal syndrome (CBS) can provide not only information about the localization and distribution of the volume loss, but also helps to understand the course and the causes of this neurodegenerative disorder. The visualization of such medical imaging data is often based on 2D sections, because they show both internal and external structures in one image. Spatial information, however, is lost. 3D visualization of imaging data is capable to solve this problem, but it faces the difficulty that more internally located structures may be occluded by structures near the surface. Here, we present an application with two designs for the 3D visualization of the human brain to address these challenges. In the first design, brain anatomy is displayed semi-transparently; it is supplemented by an anatomical section and cortical areas for spatial orientation, and the volumetric data of volume loss. The second design is guided by the principle of importance-driven volume rendering: A direct line-of-sight to the relevant structures in the deeper parts of the brain is provided by cutting out a frustum-like piece of brain tissue. The application was developed to run in both, standard desktop environments and in immersive virtual reality environments with stereoscopic viewing for improving the depth perception. We conclude that the presented application facilitates the perception of the extent of brain degeneration with respect to its localization and affected regions.

International Journal of Medical Robotics and Computer Assisted Surgery (2013)

Virtual reality-based simulators offer a cost-effective and efficient alternative to traditional medical training and planning. Developing a simulator that enables the training of medical skills and also supports recognition of errors made by the trainee is a challenge. The first step in developing such a system consists of error identification in the real procedure, in order to ensure that the training environment covers the most significant errors that can occur. This paper focuses on identifying the main system requirements for an interactive simulator for training bilateral sagittal split osteotomy (BSSO).
An approach is proposed based on failure mode and effects analysis (FMEA), a risk analysis method that is well structured and already an approved technique in other domains. Based on the FMEA results, a BSSO training simulator is currently being developed, which centers upon the main critical steps of the procedure (sawing and splitting) and their main errors. FMEA seems to be a suitable tool in the design phase of developing medical simulators. Herein, it serves as a communication medium for knowledge transfer between the medical experts and the system developers. The method encourages a reflective process and allows identification of the most important elements and scenarios that need to be trained.

The aim of computational neuroscience is to gain insight into the
dynamics and functionality of the nervous system by means of modeling
and simulation. Current research leverages the power of High
Performance Computing facilities to enable multi-scale simulations
capturing both low-level neural activity and large-scale interactions
between brain regions. In this paper, we describe an interactive
analysis tool that enables neuroscientists to explore data from such
simulations. One of the driving challenges behind this work is the
integration of macroscopic data at the level of brain regions with
microscopic simulation results, such as the activity of individual
neurons. While researchers validate their findings mainly by visualizing
these data in a non-interactive fashion, state-of-the-art visualizations,
tailored to the scientific question yet sufficiently general
to accommodate different types of models, enable such analyses
to be performed more efficiently. This work describes several visualization
designs, conceived in close collaboration with domain
experts, for the analysis of network models. We primarily focus on
the exploration of neural activity data, inspecting connectivity of
brain regions and populations, and visualizing activity flux across
regions. We demonstrate the effectiveness of our approach in a case
study conducted with domain experts.

Weight perception in virtual environments generally can be achieved with haptic devices. However, most of these are hard to integrate in an immersive virtual environment (IVE) due to their technical complexity and the restriction of a user's movement within the IVE. We describe two simple methods using only a wireless light-weight finger-tracking device in combination with a physics simulated hand model to create a feeling of heaviness of virtual objects when interacting with them in an IVE. The first method maps the varying distance between tracked fingers and the thumb to the grasping force required for lifting a virtual object with a given weight. The second method maps the detected intensity of finger pinch during grasping gestures to the lifting force. In an experiment described in this paper we investigated the potential of the proposed methods for the discrimination of heaviness of virtual objects by finding the just noticeable difference (JND) to calculate the Weber fraction. Furthermore, the workload that users experienced using these methods was measured to gain more insight into their usefulness as interaction technique. At a hit ratio of 0.75, the determined Weber fraction using the finger distance based method was 16.25% and using the pinch based method was 15.48%, which corresponds to values found in related work. There was no significant effect of method on the difference threshold measured and the workload experienced, however the user preference was higher for the pinch based method. The results demonstrate the capability of the proposed methods for the perception of heaviness in IVEs and therefore represent a simple alternative to haptics based methods.

Over the last twenty-five years, visualization software has evolved into robust frameworks that can be used for research projects, rapid prototype development, or as the basis of richly featured, end-user tools. In this article, new take stock of current capabilities and describe upcoming challenges facing visualization software in six categories: massive parallelization, emerging processor architectures, application architecture and data management,data models, rendering, and interaction. Further, for each of these categories, we describe evolutionary advances sufficient to meet the visualization software challenge, and posit areas in which revolutionary advances are required

A key aspect of air traffic infrastructure projects is the communication between stakeholders during the approval process regarding their environmental impact. Yet, established means of communication have been found to be rather incomprehensible. In this paper we present an application that addresses these communication issues by enabling the exploration of airplane noise emissions in the vicinity of airports in a virtual environment (VE). The VE is composed of a model of the airport area and flight movement data. We combine a real-time 3D auralization approach with visualization techniques to allow for an intuitive access to noise emissions. Specifically designed interaction techniques help users to easily explore and compare air traffic scenarios.

Pie menus are a well-known technique for interacting with 2D environments and so far a large body of research documents their usage and optimizations. Yet, comparatively little research has been done on the usability of pie menus in immersive virtual environments (IVEs). In this paper we reduce this gap by presenting an implementation and evaluation of an extended hierarchical pie menu system for IVEs that can be operated with a six-degrees-of-freedom input device. Following an iterative development process, we first developed and evaluated a basic hierarchical pie menu system. To better understand how pie menus should be operated in IVEs, we tested this system in a pilot user study with 24 participants and focus on item selection. Regarding the results of the study, the system was tweaked and elements like check boxes, sliders, and color map editors were added to provide extended functionality. An expert review with five experts was performed with the extended pie menus being integrated into an existing VR application to identify potential design issues. Overall results indicated high performance and efficient design.

In recent years, the simulation of spiking neural networks has advanced in terms of both simulation technology and knowledge about neuroanatomy. Due to these advances, it is now possible to run simulations at the brain scale, which produce an unprecedented amount of data to be analyzed and understood by researchers. As aid, VisNEST, a tool for the combined visualization of simulated spike data and anatomy was developed.

A common problem in Virtual Reality is latency. Especially for head tracking, latency can lead to a lower immersion. Prediction can be used to reduce the effect of latency. However, for good results the prediction process has to be reliably fast and accurate.
Human motion is not homogeneous and humans often tend to change the way they move.
Prediction models can be designed for these special motion types.
To combine the special models, a multiple model approach is presented.
It constantly evaluates the quality of the different specialized motion prediction and adjusts the set of motion models.
We propose two variants, and compare them to a reference prediction algorithm.

The visual analysis of brain volume data by neuroscientists is commonly done in 2D coronal, sagittal and transversal views, limiting the visualization domain from potentially three to two dimensions. This is done to avoid occlusion and thus gain necessary context information. In contrast, this work intends to benefit from all spatial information that can help to understand the original data. Example data of a patient with brain degeneration are used to demonstrate how to enrich 2D with 3D data. To this end, two approaches are presented. First, a conventional 2D section in combination with transparent brain anatomy is used. Second, the principle of importance-driven volume rendering is adapted to allow a direct line-of-sight to relevant structures by means of a frustum-like cutout.

In modeling and simulation of manufacturing processes, complex models are used to examine and understand the behavior and properties of the product or process. To save computation time, global approximation models, often referred to as metamodels, serve as surrogates for the original complex models. Such metamodels are difficult to interpret, because they usually have multi-dimensional input and output domains. We propose a hyperslice-based visualization approach, that uses hyperslices in combination with direct volume rendering, training point visualization, and gradient trajectory navigation, that helps in understanding such metamodels. Great care was taken to provide a high level of interactivity for the exploration of the data space.

With the introduction of complex precomputed scattering tables by Bruneton in
2008, the quality of visualizing atmospheric scattering vastly improved. The presented algorithms
allowed for the rendering of complex atmospheric features such as multiple-scattering
or light shafts in real-time and at interactive framerates. While their published implementation
corresponding to the publication was merely a proof of concept, we present a more
practical approach by applying their scattering theory to an already existing planetary rendering
engine. Because the commonly used set of parameters only describes the atmosphere
of the Earth, we further extend the scattering formulation to visualize the atmosphere of
the planet Mars. Validating the modified scattering and resulting parameters is then done
by comparison with available imagery from the Martian atmosphere

While visual feedback is dominant in Virtual Environments, the use of other modalities like haptics and acoustics can enhance believability, immersion, and interaction performance. Haptic feedback is especially helpful for many interaction tasks like working with medical or precision tools. However, unlike visual and auditory feedback, haptic reproduction is often difficult to achieve due to hardware limitations. This article describes a user study to examine how auditory feedback can be used to substitute haptic feedback when interacting with a vibrating tool. Participants remove some target material with a round-headed drill while avoiding damage to the underlying surface. In the experiment, varying combinations of surface force feedback, vibration feedback, and auditory feedback are used. We describe the design of the user study and present the results, which show that auditory feedback can compensate the lack of haptic feedback.

Eurographics Workshop on Visual Computing for Biology and Medicine (2012)

Brightness modulation (B-Mode) ultrasound (US) images are used to visualize internal body structures during diagnostic and invasive procedures, such as needle insertion for Regional Anesthesia. Due to patient availability and health risks-during invasive procedures-training is often limited, thus, medical training simulators become a viable solution to the problem. Simulation of ultrasound images for medical training requires not only an acceptable level of realism but also interactive rendering times in order to be effective. To address these challenges, we present a generative method for simulating B-Mode ultrasound images using surface representations of the body structures and geometrical acoustics to model sound propagation and its interaction within soft tissue. Furthermore, physical models for backscattered, reflected and transmitted energies as well as for the beam profile are used in order to improve realism. Through the proposed methodology we are able to simulate, in real-time, plausible view- and depth-dependent visual artifacts that are characteristic in B-Mode US images, achieving both, realism and interactivity.

Modeling and simulating a brain’s connectivity produces an immense
amount of data, which has to be analyzed in a timely fashion.
Neuroscientists are currently modeling parts of the brain –
e.g. the visual cortex – of primates like Macaque monkeys in order
to deduce functionality and transfer newly gained insights to
the human brain. Current research leverages the power of today’s
High Performance Computing (HPC) machines in order to simulate
low level neural activity. In this paper, we describe an interactive
analysis tool that enables neuroscientists to visualize the resulting
simulation output. One of the driving challenges behind our development
is the integration of macroscopic data, e.g. brain areas, with
microscopic simulation results, e.g. spiking behavior of individual neurons.

International Masaryk Conference for Ph.D. Students and Young Researchers (2012)

Correspondence Analysis (CA) is frequently used to interpret correlations between categorical variables in the area of market research. To do so, coherences of variables are converted to a three-dimensional point cloud and plotted as three different 2D-mappings. The major challenge is to correctly interpret these plottings. Due to a missing axis, distances can easily be under- or overestimated. This can lead to a misclustering and misinterpretation of data and thus to faulty conclusions. To address this problem we present CAVIR, an approach for CA in Virtual Reality. It supports users with a virtual three-dimensional representation of the point cloud and different options to show additional information, to measure Euclidean distances, and to cluster points. Besides, the free rotation of the entire point cloud enables the CA user to always have a correct view of the data.

Correspondence Analysis (CA) is used to interpret correlations between categorical variables in the areas of social science and market research. To do so, coherences of variables are converted to a three-dimensional point cloud and plotted as several different 2D-mappings, each containing two axes. The major challenge is to correctly interpret these plottings. Due to a missing axis, distances can easily be under- or overestimated. This can lead to a misinterpretation and thus a misclustering of data.
To address this problem we present CAVIR, an approach for CA in Virtual Reality. It supports users with a three-dimensional representation of the point cloud and different options to show additional information, to measure Euclidean distances, and to cluster points. Besides, the motion parallax and a free rotation of the entire point cloud enable the CA expert to always have a correct view of the data.

In this contribution, we present an immersive visualization of room acoustical simulation data. In contrast to the commonly employed external viewpoint, our approach places the user inside the visualized data. The main problem with this technique is the occlusion of some data points by others. We present different solutions for this problem that allow an interactive analysis of the simulation data.

In this paper we present a simulator for two-handed haptic interaction. As an application example, we chose a medical scenario that requires simultaneous interaction with a hand and a needle on a simulated patient. The system combines bimanual haptic interaction with a physics-based soft tissue simulation. To our knowledge the combination of finite element methods for the simulation of deformable objects with haptic rendering is seldom addressed, especially with two haptic devices in a non-trivial scenario. Challenges are to find a balance between real-time constraints and high computational demands for fidelity in simulation and to synchronize data between system components. The system has been successfully implemented and tested on two different hardware platforms: one mobile on a laptop and another stationary on a semi-immersive VR system. These two platforms have been chosen to demonstrate scaleability in terms of fidelity and costs. To compare performance and estimate latency, we measured timings of update loops and logged event-based timings of several components in the software.

A major challenge in Virtual Reality is to enable users to efficiently explore virtual environments, regardless of prior knowledge. This is particularly true for complex virtual scenes containing a huge amount of potential areas of interest. Providing the user convenient access to these areas is of prime importance, just like supporting her to orient herself in the virtual scene. There exist techniques for either aspect, but combining these techniques into one holistic system is not trivial.
To address this issue, we present the Hierarchy Browser. It supports the user in creating a mental image of the scene. This is done by offering a well-arranged, hierarchical visual representation of the scene structure as well as interaction techniques to browse it. Additional interaction allows to trigger a scene manipulation, e.g. an automated travel to a desired area of interest. We evaluate the Hierarchy Browser by means of an expert walkthrough.

Conventional beam tracing can be used for solving global illumination problems. It is an efficient algorithm, and performs very well when implemented on the GPU. This allows us to apply the algorithm in a novel way to the problem of radio wave propagation. The simulation of radio waves is conceptually analogous to the problem of light transport. We use a custom, parallel rasterization pipeline for creation and evaluation of the beams. We implement a subset of a standard 3D rasterization pipeline entirely on the GPU, supporting 2D and 3D framebuffers for output. Our algorithm can provide a detailed description of complex radio channel characteristics like propagation losses and the spread of arriving signals over time (delay spread). Those are essential for the planning of communication systems required by mobile network operators. For validation, we compare our simulation results with measurements from a real world network. Furthermore, we account for characteristics of different propagation environments and estimate the influence of unknown components like traffic or vegetation by adapting model parameters to measurements.

We present a comprehensive 3D sketch recognition framework for interaction within Virtual Environments that allows to trigger commands by drawing symbols, which are recognized by a multi-level analysis. It proceeds in three steps: The segmentation partitions each input line into meaningful segments, which are then recognized as a primitive shape, and finally analyzed as a whole sketch by a symbol matching step. The whole framework is configurable over well-defined interfaces, utilizing a fuzzy logic algorithm for primitive shape learning and a textual description language to define compound symbols. It allows an individualized interaction approach that can be used without much training and provides a good balance between abstraction and intuition. We show the real-time applicability of our approach by performance measurements.

Proceedings of the International Symposium on Room Acoustics (ISRA), 2010

During the last decade, Virtual Reality (VR) systems have progressed from primary laboratory experiments into serious and valuable tools. Thereby, the amount of useful applications has grown in a large scale, covering conventional use, e.g., in science, design, medicine and engineering, as well as more visionary applications such as creating virtual spaces that aim to act real. However, the high capabilities of today’s virtual reality systems are mostly limited to firstclass visual rendering, which directly disqualifies them for immersive applications. For general application, though, VR-systems should feature more than one modality in order to boost its range of applications. The CAVE-like immersive environment that is run at RWTH Aachen University comprises state-of-the-art visualization and auralization with almost no constraints on user interaction. In this article a summary of the concept, the features and the performance of our VR-system is given. The system features a 3D sketching interface that allows controlling the application in a very natural way by simple gestures. The sound rendering engine relies on present-day knowledge of Virtual Acoustics and enables a physically accurate simulation of sound propagation in complex environments, including important wave effects such as sound scattering, airborne sound insulation between rooms and sound diffraction. In spite of this realistic sound field rendering, not only spatially distributed and freely movable sound sources and receivers are supported, but also modifications and manipulations of the environment itself. The auralization concept is founded on pure FIR filtering which is realized by highly parallelized non-uniformly partitioned convolutions. A dynamic crosstalk cancellation system performs the sound reproduction that delivers binaural signals to the user without the need of headphones. The significant computational complexity is handled by distributed computation on PCclusters that drive the simulation in real-time even for huge audio-visual scenarios.

Beam tracing can be used for solving global illumination problems. It is an efficient algorithm, and performs very well when implemented on the GPU. This allows us to apply the algorithm in a novel way to the problem of radio wave propagation. The simulation of radio waves is conceptually analogous to the problem of light transport. However, their wavelengths are of proportions similar to that of the environment. At such frequencies, waves that bend around corners due to diffraction are becoming an important propagation effect. In this paper we present a method which integrates diffraction, on top of the usual effects related to global illumination like reflection, into our beam tracing algorithm. We use a custom, parallel rasterization pipeline for creation and evaluation of the beams. Our algorithm can provide a detailed description of complex radio channel characteristics like propagation losses and the spread of arriving signals over time (delay spread). Those are essential for the planning of communication systems required by mobile network operators. For validation, we compare our simulation results with measurements from a real world network.

We present a novel method for efficient computation of complex channel characteristics due to multipath effects in urban microcell environments. Significant speedups are obtained compared to state-of-the-art ray-tracing algorithms by tracing continuous beams and by using parallelization techniques. We optimize simulation parameters using on-site measurements from real world networks. We formulate the adaption of model parameters as a constrained least-squares problem where each row of the matrix corresponds to one measurement location, and where the columns are formed by the beams that reach the respective location.